During my PhD I worked with zebra finches, a bird which is commonly kept as a pet and in flocks (being a social species). Even though I spent an awful lot of time with these little birds (usually six days a week, including many of my Friday nights), I never learned to tell individuals apart, except for the occasional unfortunate mutant. However, this is hardly surprising since we as humans haven’t evolved to tell individuals of other species apart. Instead, we are really good at telling individuals of our own species apart; think for a minute about all the faces you can remember, including individuals you may have met only once, years ago. The reason for our superior facial recognition skills is likely because, as a social species, learning and remembering who is who, is very important in getting along. To make friends, impress people and find a mate, being able to recognise people is generally considered a good thing (think of the humiliation when someone remembers you but you don’t remember them).

The same is true for other social species. One study that received a lot of media attention a few years ago showed that wasps could recognise each other’s’ faces. Now, a recent study just published in Animal Behaviour has found that zebra finches also recognise each other’s faces. Zebra finches are socially monogamous, building nests and breeding together for multiple breeding seasons. However, when not breeding they exist in flocks of up to 300 birds. Therefore, it would seem highly likely that individuals would be able to recognise their mates in order to mate with them again the following season. It’s been known that females do know the sound of their male partner (what he sounds like when he sings his song), but the researchers wanted to know if females could also identify their partners from his visual appearance.

Fleischman and colleagues from Tel-Aviv University trained these birds through a number of steps to respond to pictures of each other on a digital screen. Once trained to peck at the screen for a food reward, the female was then trained to peck at a photo of her mate for a food reward. She was also shown photos of an unknown male, and was not rewarded for pecking at him. To test whether the female had actually learned to identify the male, and not just a single photo, the female was then shown four new photos: two of her male and two of the unknown male. The females pecked at the photos of their partners, showing that they had learned what these males looked like.

Male zebra finches. Photo: Felicity Muth

Next, the researchers wanted to see if females could do this for photos of any male they knew, or if it was specific to their mate. To do this they repeated the experiment, but this time using photos of a male from the female’s flock who wasn’t her mate. They first tested females who lived in small flocks, then females who lived in large flocks (consisting of 30 birds).

Female zebra finches pecked at the photo of their male partner on a digital screen. Credit: Fleischman et al. 2016

Interestingly, it seems that zebra finch females were able to recognise the faces of males when they lived with them in small flocks, but not when they lived with them in larger flocks. What’s more, they were much better at recognising the face of their male partner than of another male in their small flock.

Why might it be that it's harder to train females to recognise males from larger groups? One possibility is that because even when zebra finches live in larger flocks, they tend to make smaller sub-groups that they hang around in. Thus the males that were shown to the females from the larger group may have been very socially distant to them. It is also likely that in ‘real life’ the females also use other cues to recognise males (like their songs) and that the visual cue on the screen isn’t as salient as seeing the males in real life (just as for us, sometimes it can be harder to recognise someone in a photo than in real life).

The researchers point out that they would now like to know which specific facial characteristics females pay attention to; is it the whole face or just a particular pattern on the zebra finch’s cheek? Also, can males recognise females, in addition to other males in their flock? It will be interesting to see whether other social species like the zebra finch use similar visual cues to the ones we do when identifying each other, and if not, why this might be different.

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